As you saw in this book, Azure Stack is the optimal basis for running Azure workloads on your own or your service providers' private cloud solution, mostly connected to the Azure public. As of today, Microsoft is the only cloud vendor that provides a hybrid cloud solution with 1:1, which the same technology that is running on Azure today.
In regard to TCO and RoI, there is a great option to order not just Azure Stack as a software and be responsible for setting it up by yourself and making it run properly. This could mean weeks and months for the deployment. Azure Stack comes with the hardware solution as an integrated solution. You would only have to set it up by connecting it to the internet, power it on, and provide cooling and rack space. So, it may take only a few days to have Azure Stack up and running and in place.
The more interesting point, then, is to design your services in a way you would really need them. This solution design is not a technical deep dive; it is more a technical service design. Finally, these solutions will need to result in Azure Resource Manager templates using PaaS or IaaS solutions. They could be private or public only; additionally, they could he hybrid, and based on the workloads, they will mostly be hybrid. If something happens in a service that runs after the completely deployment, PowerShell DSC is your friend.
From the administration point of view, there is a wide variety of tools, starting with the ARM portal and leading to CLI, PowerShell modules, or even Visual Studio. The same administrative tools as Azure means that the administrators do not have to learn different technologies--everything is the same. This reduces training costs enormously; it even means that your IT staff would be able to run these technologies because otherwise, a different cloud service means a different cloud technology. The only thing you would need to be responsible for is the administrative part (maintaining the hardware, and so on).
Finally, there are a lot of technologies that would need to make the IT world more comparable and would lead to an industrial IT revolution. This is already in the middle of taking place, and you and your IT needs to deal with it. Azure Stack is the product of the future, which will give you all the technology to go with the cloud and go with it on a hybrid layer.